UPDATE: CHP investigating 'unusual' death on I-5

California Highway Patrol officers are trying to piece together the "unusual" death of a man along Interstate 5 Sunday.

Officer Jason Morton said the victim had been a passenger in a car, but somehow ended up getting hit and killed by a big rig around noon Sunday near Lakehead. The incident happened just south of the town on the northbound side of the freeway.

Coroner's officials on Thursday identified the victim as 31-year-old Benjamin Kennedy Riney, of San Francisco.

While Riney may have ended up getting hit in traffic, Morton said whatever caused him to get out of the car wasn't related to an accident.

"The car didn’t crash, so that’s what they’re trying to figure out," Morton said. "Somehow, he came out of that car without being involved in a crash."

Adding to the mystery, Morton said the semi hit and killed Riney after traffic had slowed in the area in response to whatever was going on with the car he was in.

"Traffic got snarled from this happening ... getting hit by a big rig was when everything was at a slow speed," he said. "So I don't know if something else happened again there."

The man driving the car carrying Riney stayed on the scene and gave a statement, Morton said, but officers are still trying to contact outside witnesses to get a complete picture. Morton said he didn't know what the driver told responding officers, and he believes there were only the two men in the car.